Axially staged annular combustion chamber of a gas turbine

ABSTRACT

An axially stepped annular combustion chamber, especially of an aircraft gas turbine, has an essentially independent main combustion chamber 5&#39; as well as an independent pilot burner chamber 5. An appropriate design of internal limiting walls 6a, 6b of pilot burner chamber 5 ensures that the combustion gases enter the main burner zone 5&#39; essentially in the radial direction. This ensures optimum mixing of the fuel with air in this main combustion zone and/or main combustion chamber 5&#39;, thus minimizing exhaust emissions and ensuring optimum temperature distribution at combustion chamber outlet 8. Internal limiting wall 6a can have a deflecting section 12 or outer wall section 6b can run at an angle to pilot burner lengthwise axis 3a, so that the cross section of pilot burner zone 5 is reduced in the flow direction.

This application is a 371 of PCT/EP96/00895 filed Mar. 4, 1996.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an axially staged annular combustion chamber ofa gas turbine with a central axis, and with a plurality of pilot burnerslocated between annular wall sections, as well as with main burners thatterminate in the combustion chamber downstream from and radially outsidethe pilot burners. A main burner zone abuts the main burners. Thecombustion chamber includes an outer and an inner combustion chamberwall, each annular in shape. Each of the walls extends up to thecombustion chamber outlet, with the inner combustion chamber wall havinga wall section that runs essentially parallel to the pilot burner axisin the area of the pilot burner zone.

Regarding known prior art, reference is made for example to WO 93/25851(having a U.S. equivalent in U.S. Pat. No. 5,406,799) or German Patentdocument DE-OS 28 38 258, but especially to GB-A-2 010 408 (having aU.S. equivalent in U.S. Pat. No. 4,194,358), showing an axially stagedannular combustion chamber in which the combustion gases of the pilotburner zone are conducted by an appropriate design, especially of theinner combustion chamber wall, into the main burner zone.

The goal of the present invention is to improve an axially stagedannular combustion chamber of the above-mentioned type, especially inregard to the mixing of the pilot burner gases with the main burnergases and thus to the exhaust emissions and/or the temperaturedistribution in the vicinity of the combustion chamber outlet.

To achieve this goal, provision is made such that the inner combustionchamber wall, adjoining the inner wall section that forms the pilotburner zone and essentially also runs parallel to the central axis, hasa deflecting section that is convex-concave in shape. The deflectingsection runs toward the main burner zone as viewed looking downstream,i.e. as viewed from inside the combustion chamber. The deflectingsection, viewed in the radial direction relative to the central axis,extends approximately at the level of the outer pilot burner wallsection. The deflecting section is abutted by a wall section that leadsto the combustion chamber outlet and runs essentially parallel to thecentral axis.

An additional measure consists in that the outer wall section of thepilot burner zone that faces the main burner runs at an angle to thelengthwise axis of the associated pilot burner, so that the crosssection of the pilot burner zone decreases in the flow direction.Advantageous improvements and embodiments are described herein.

The invention will now be described in greater detail with reference totwo preferred embodiments as shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial lengthwise section through an annular combustionchamber according to the invention;

FIG. 2 shows a partial lengthwise section through an annular combustionchamber according to the invention; and

FIG. 3 shows two possible partial cross sections through an annularcombustion chamber according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 2, reference number 1 indicates the centralaxis of a basically known annular combustion chamber 2, especially anaircraft gas turbine. A plurality of pilot burners 3 as well as severalmain burners 4 are located in annular combustion chamber 2, distributedaround its circumference. Main burners 4 as usual are arrangedexternally in the radial direction and, in one preferred embodiment, canhave their lengthwise axes or main burner axes 4a inclined with respectto lengthwise axes 3a of pilot burners 3, in other words, inclinedrelative to so-called pilot burner axes 3a. The main burners 4 locatedin the radial direction outside pilot burners 3 thus terminate incombustion chambers 2 downstream from pilot burners 3. A so-called pilotburner zone 5 adjoins pilot burners 3 while a so-called main burner zone5' is formed directly downstream of main burners 4.

The entire combustion chamber 2, in other words the unit composed ofpilot burner zone 5 and main burner zone 5', is delimited by an externalannular combustion chamber wall 10 and is delimited from central axis 1by an internal combustion chamber wall 11. Wall 11 consists ofindividual so-called wall sections, namely of an inner wall section 6aassociated with pilot burner zone 5 and, in the embodiment shown in FIG.1, of an adjoining so-called deflecting section 12. In both embodiments,the wall 11 consists of a wall section 13 that leads to combustionchamber outlet 8 (outlet 8 can also be referred to as combustion chamberend 8). Pilot burner zone 5 is delimited externally in the radialdirection by an outer wall section 6b that extends up to main burner 4.Outer wall section 6b is adjoined by main burner or burners 4, with eachmain burner 4 or each main burner axis 4a being arranged at an angle tothe pilot burner axis 3a of each pilot burner 3, as is clearly shown.Downstream, far outside the combustion chamber, the two lengthwise axes3a, 4a of burners 3, 4 would intersect, while lengthwise axis 3a isaligned essentially parallel to central axis 1. However, thisarrangement only relates to the embodiments shown here; of course, itwould also be possible to arrange the individual lengthwise axes 3a, 4aof pilot burners 3 and/or main burners 4 differently (parallel to oneanother, for example). In addition, pilot burners 3 and main burners 4do not necessarily have to be in a common lengthwise section plane asshown here, but pilot burner 3 and main burner 4 can also be arrangedstaggered with respect to one another in the circumferential direction.Moreover, the flow direction of the combustion gases in combustionchamber 2 is also indicated by arrow 7.

In addition, a further outermost wall section 6c of the outer annularcombustion chamber wall 10 is provided between main burner 4 andcombustion chamber outlet 8.

The primary point of importance here is the pattern of the internalcombustion chamber wall 11. This wall, in the embodiment shown in FIG.1, has a deflecting section 12 that runs toward main burner zone 5',abutting wall section 6a that forms pilot burner zone 5. This deflectingsection 12 is aligned at least partially in the radial direction (thisis defined as being perpendicular to central axis 1), i.e. deflectingsection 12 intersects central axis 1 in the embodiment shown here at anangle of approximately 45° for example. This means that the combustiongases from pilot burners 3, guided by this deflecting section 12, entermain burner zone 5' essentially in the radial direction. This shape ofinternal combustion chamber wall 11 can also be described specificallyby saying that this combustion chamber wall 11 is concave-convex inshape in the area of deflecting section 12 as well as relative tocombustion chamber 2, in other words as viewed from the interior of thecombustion chamber, looking downstream (namely in flow direction 7).This means that, starting at wall section 6a, a concave curvature isinitially provided in deflecting section 12, which is abutted by a wallsection 13 with a convex curvature that leads to combustion chamberoutlet 8. This design ensures optimum mixing of the fuel that entersmain burner zone 5' through main burner 4 with air in main burner zone5'. As a result, the exhaust emissions are minimized and the temperaturedistribution at combustion chamber outlet 8 can be matched with thatfrom a non-stepped combustion chamber.

An additional measure for achieving a better mixture of the pilot burnergases with the main burner gases is shown in FIG. 2, where for the sakeof simplicity the deflecting section according to the invention,designated by reference number 12 in FIG. 1, is not shown.

In FIG. 2, outer wall section 6b of pilot burner zone 5, facing mainburner 4, is inclined relative to lengthwise axis 3a of associated pilotburner 3 in such fashion that the cross section D of pilot burner zone 5is decreased in the flow direction, in other words from pilot burner 3in the direction of arrow 7 toward the center of combustion chamber 2.This means that the main burner 4 is immersed in, or penetrates, pilotburner zone 5 so to speak, as is especially apparent from FIG. 2 in theform of a so-called penetration depth Δ.

This reduction in the cross section D of pilot burner zone 5 and/or thispenetration of main burner 4 into pilot burner zone 5 firstly producesan especially good mixing of the main burner gases with the gases ofpilot burner 3, since the latter undergo an advantageous change in theirflow field. The pilot burner gases are vorticized to a greater degree byouter wall section 6b and are additionally accelerated by the reductionin cross section. Improved mixing at the center of combustion chamber 2with the gas flows emitted from main burner 4 therefore results.

In addition, the axially staged annular combustion chambers 2 accordingto the invention described here can also be referred to basically as anassembly of two independent non-stepped annular burners. This means thatboth main burner zone 5' and pilot burner zone 5 each exhibit the designfeatures of non-stepped annular combustion chambers and therefore areoptimized for the upper load range (for main burner zone 5') and for thelower load range (for pilot burner zone 5) of the gas turbine. As can beseen, main burner zone 5' located outward is designed in the same way asa conventional non-stepped annular combustion chamber, with main burneraxis 4a essentially pointing in the direction of the combustion chamberaxis or coinciding therewith. In addition, streams of mixed air 9 areadded and mixed in main burner zone 5' and in annular combustion chamber2 on both sides, in other words, from inside and from outside (this isonly shown in FIG. 1) as is usual in conventional annular combustionchambers. In addition, in this (conventional) annular combustion chamber2, a coupled pilot burner zone 5 is also provided, i.e. a sort ofseparate pilot burner chamber that is located radially inward as well asupstream from main burner zone 5'. In order to be able to conduct thecombustion gases from this pilot burner chamber or pilot burner zone 5optimally into main burner zone 5' and thus permit optimum mixing offuel and air in said zone 5', an effort can be made to ensure that thecombustion gases from the pilot burner chambers enter main burner zone5' and/or the corresponding main burner chambers essentially in theradial direction. This radial direction determination takes place inFIG. 1 as a result of the so-called deflecting section 12 of innerannular combustion chamber wall 11, while in FIG. 2 the pilot burnergases undergo increased vorticization as a result of the change in theflow field and are accelerated toward the main burner gases.

Advantageously, especially with the design of annular combustion chamber2 that is shown and described in FIG. 2, an extremely compact form isalso achieved, i.e. the diameter of an annular combustion chamber ofthis type and/or its so-called structural height can be minimized as aresult. This leads to favorable conditions when the value of thepenetration depth Δ relative to the cross section D* of pilot burnerzone 5 in the area of pilot burners 3 lies in the range from 0.1 to 0.3,in other words, 0.1≦Δ/D*≦0.3. The compact design is further promoted bythe staggered arrangement, shown in FIG. 3 as well, of pilot burners 3as well as main burners 4. Then there is, so to speak, a pilot burner 3between each two main burners 4.

FIG. 2 also shows that inside wall section 6a of pilot burner zone 5 canrun at an angle in its end area relative to pilot burner lengthwise axis3a, so that outer wall section 6b as well as inner wall section 6a runtogether, so to speak, in the end areas of said sections. Once again,this causes a desired reduction in the cross section of pilot burnerzone 5, with this slope of the inner combustion chamber wall 11 beingable to continue with essentially the same orientation up to combustionchamber end 8, and thus, with the same orientation, limiting the entireannular combustion chamber 2 on the inside. The outer combustion chamberwall 10 that delimits annular combustion chamber 2 in the area betweenmain burner 4 and combustion chamber end 8 can be shaped in accordancewith the most favorable design. Here again it is recommended to use apattern for wall section 6c that converges toward lengthwise axis 4ainitially in the area that directly abuts main burner 4, while in thevicinity of combustion chamber end area 8 there must be a sufficientcross section for the gases that are escaping, and thus a pattern may berequired that diverges relative to central axis 1.

Outer wall section 6b of pilot burner zone 5, in both FIG. 1 and FIG. 2,also extends in the same manner as the entire annular combustion chamber2, namely essentially annularly, but this does not mean that thereduction in cross section of pilot burner zone 5 over essentially theentire annular combustion chamber 2 must be performed to the same degreeall the way around, although this is quite possible. Instead,quasi-shell-shaped depressions can be provided only in the vicinity ofmain burner 4, in outer wall section 6b which otherwise runs essentiallyparallel to pilot burner lengthwise axis 3. This latter design is shownschematically in the lower half of FIG. 3, while the first designmentioned is shown in the upper half of FIG. 3, which showsschematically a view taken in the direction of arrow X from FIG. 2.While the reduction in cross section of pilot burner zone 5 is performedby shell-shaped depressions, the reduction in cross section of pilotburner zone 5 is provided primarily in the planes formed by lengthwiseaxes 4a of main burners 4 as well as central axis 1 of annularcombustion chamber 2.

Especially in the embodiment shown in FIG. 1, wall section 13 of innercombustion chamber wall 11 that abuts deflecting section 12 downstreamthereof and leads to combustion chamber outlet 8 is once again alignedessentially parallel to main burner axis 4a and/or essentially in thedirection of central axis 1. This wall section 13 is thereforeessentially once again a part of main burner zone 5' and/or thecorresponding main combustion chamber. The pilot burner zone 5 on theother hand, looking in flow direction 7, terminates in the vicinity ofdeflecting section 12. In this pilot burner zone 5, a short distanceupstream from deflecting section 12, mixed air streams (as shown byarrows 14) can be supplied both internally and externally a shortdistance upstream from main burner 4 through openings, not shown ingreater detail, in combustion chamber wall 11.

Of course, the precise dimensions as well as the angles that individualwall sections 6a, 6b, 12, and 13 form with one another can be designedto be completely different from the embodiment shown without departingfrom the spirit and scope of the present invention. Similarly,additional variations from the embodiment shown are possible. Thus, awide variety of fuel atomization concepts can be used for pilot burners3 as well as for main burners 4, and similarly the openings and/or holesfor mixed air streams 9 and 14 can be located differently. In addition,these mixed air streams 9, 14 can be supplied twisted (swirled) or nottwisted, without this having enormous consequences as regards thesignificant advantages of the present invention, namely optimal mixingespecially in main burner zone 5'.

What is claimed:
 1. An axially staged annular combustion chamber of agas turbine having a central axis, comprising:a plurality of pilotburners arranged between inner and outer annular wall sections; mainburners having ends terminating downstream of said plurality of pilotburners and being located radially outward from said pilot burners insaid combustion chamber, said main burners abutting a main burner zonehaving outer and inner combustion chamber walls which are both annularin shape and extend up to a combustion chamber outlet, said innercombustion chamber wall in an area of a pilot burner zone forming theinner annular wall section running essentially parallel to a pilotburner axis; wherein said inner combustion chamber wall abuts the innerannular wall section, which forms the pilot burner zone and runsessentially in parallel to the central axis, said inner combustionchamber wall having a deflecting section which is convex-concave inshape and runs toward the main burner zone relative to the combustionchamber when viewed in a downstream direction; and wherein saiddeflection section, when viewed in a radial direction relative to acentral axis, ends approximately at a radial level of the outer annularwall section and abuts a downstream wall section of the inner combustionchamber wall defining the main burner zone leading to the combustionchamber outlet.
 2. The annular combustion chamber according to claim 1,wherein combustion gases from the plurality of pilot burners are guidedby the deflecting section so as to enter the main burner zoneessentially in a radial direction.
 3. The annular combustion chamberaccording to claim 1, wherein the outer annular wall section of thepilot burner zone faces the main burners, said outer annular wallsection extending at an angle relative to a lengthwise axis of anassociated pilot burner, such that a cross section of the associatedpilot burner zone is reduced in a flow direction.
 4. The annularcombustion chamber according to claim 2, wherein the outer annular wallsection of the pilot burner zone faces the main burners, said outerannular wall section extending at an angle relative to a lengthwise axisof an associated pilot burner, such that a cross section of theassociated pilot burner zone is reduced in a flow direction.
 5. Theannular combustion chamber according to claim 3, wherein the innerannular wall section is also arranged at an angle in an end arearelative to the lengthwise axis such that the cross-section of the pilotburner zone is reduced in the flow direction due to convergent inner andouter annular wall sections.
 6. The annular combustion chamber accordingto claim 4, wherein the inner annular wall section is also arranged atan angle in an end area relative to the lengthwise axis such that thecross-section of the pilot burner zone is reduced in the flow directiondue to convergent inner and outer annular wall sections.
 7. The annularcombustion chamber according to claim 3, wherein a penetration depthsize of the main burner into the pilot burner zone resulting from thereduced cross-section of the pilot burner zone, relative to a reducedcross-section of the pilot burner zone in the area of the pilot burneris within a range of 0.1 to 0.3.
 8. The annular combustion chamberaccording to claim 5, wherein a penetration depth size of the mainburner into the pilot burner zone resulting from the reducedcross-section of the pilot burner zone, relative to a reducedcross-section of the pilot burner zone in the area of the pilot burneris within a range of 0.1 to 0.3.
 9. The annular combustion chamberaccording to claim 3, wherein the reduced cross-section of the pilotburner zone is primarily formed in planes containing a lengthwise mainburner axes and the central axis of the annular combustion chamber. 10.The annular combustion chamber according to claim 5, wherein the reducedcross-section of the pilot burner zone is primarily formed in planescontaining a lengthwise main burner axes and the central axis of theannular combustion chamber.
 11. The annular combustion chamber accordingto claim 7, wherein the reduced cross-section of the pilot burner zoneis primarily formed in planes containing a lengthwise main burner axesand the central axis of the annular combustion chamber.
 12. The annularcombustion chamber according to claim 3, wherein the reducedcross-section of the pilot burner zone is essentially provided allaround the annular combustion chamber.
 13. The annular combustionchamber according to claim 5, wherein the reduced cross-section of thepilot burner zone is essentially provided all around the annularcombustion chamber.
 14. The annular combustion chamber according toclaim 7, wherein the reduced cross-section of the pilot burner zone isessentially provided all around the annular combustion chamber.
 15. Theannular combustion chamber according to claim 1, wherein said mainburners and said plurality of pilot burners are staggered with respectto one another in a circumferential direction.
 16. The annularcombustion chamber according to claim 1, further comprising openings inthe outer annular wall section and the inner combustion chamber wallthrough which air is provided, a downstream end of the pilot burner zonebeing defined by the supplied air.
 17. The annular combustion chamberaccording to claim 1, wherein the downstream wall section runssubstantially parallel to or slightly divergent from the central axis,leading to the combustion chamber outlet.
 18. A combustion chamber wallarrangement of a gas turbine having a central axis and at least onepilot burner and a radially outwardly and downstream arranged mainburner, comprising:an inner combustion chamber wall including an innerwall section having an inner surface extending substantially parallel toboth an associated burner axis and the central axis, a deflecting wallsection having an inner surface with a convex-concave shape adjoiningsaid inner wall section at a downstream end, and a final wall sectionadjoining said deflecting wall section at a downstream end at a greaterradial distance from the central axis than the radial distance of saidinner wall section, said final wall section forming a part of anassociated burner zone and ending at a combustion chamber outlet area;and an outer combustion chamber wall.
 19. The combustion wallarrangement according to claim 18, wherein said outer combustion chamberwall comprises an outer annular wall section which, together with saidinner wall section defines a further burner zone, said outer annularwall section being arranged at a radial distance from the central axisapproximately at the same radial distance of said final wall section.20. The combustion wall arrangement according to claim 19, wherein saidouter annular wall section extends at an angle relative to a lengthwiseaxis of said defined further burner zone such that a cross-section ofsaid defined further burner zone is reduced in a downstream flowdirection.
 21. The annular combustion chamber according to claim 18,wherein the downstream wall section runs substantially parallel to orslightly divergent from the central axis, leading to the combustionchamber outlet.